A device-to-device (D2D) communication manner refers to that a transmit end directly sends data to a receive end by using an electromagnetic wave, and the data does not need to be forwarded by a base station or a cellular network. However, restricted by factors such as power consumption and interference of user equipment (UE), a communication distance of this communication manner is limited. In addition, user equipment outside coverage of a network (for example, a case of partial coverage) cannot establish a connection to the network. As a result, a capability of communication between the user equipment and the network is affected. Therefore, user equipment inside the coverage of the network may be used as first UE, namely, relay user equipment (Relay UE), configured to provide a relay service; and user equipment outside the coverage of the network may be used as second UE, namely, remote user equipment (Remote UE). When the remote user equipment is outside the coverage of the network and is relatively near a coverage area of the network, the remote user equipment may establish a connection to the network by using the relay user equipment.
In a multi-UE coordination technology, when same second UE simultaneously provides a relay service for multiple first UEs, data is transmitted between the multiple first UEs and an evolved base station (eNB) by using the second UE. The transmitted data may include signaling data or service data. The signaling data is a control signal visible to an access network. The service data is data other than the signaling data of data transmitted in a system, and is, for example, data transmitted in a core network or data transmitted on an application layer. The eNB cannot distinguish whether the received data is the signaling data or the service data, and cannot distinguish specific first UE that is a source transmit end of the received data either.